1. Field of the Invention
The present invention relates to a fuel-feeding device and a pressure control valve (a pressure regulator) used in the fuel-feeding device.
2. Description of Related Art
A fuel-feeding device is taught, for example, by Japanese Laid-Open Patent Publication No. 2002-235622. As shown in FIG. 8, this fuel-feeding device includes a fuel pump 1, fuel feeder passages LF1 and LF2, a back pressure generating passage LC having a solenoid valve S, and a pressure control valve 2 (a pressure regulator). The fuel pump 1 is arranged and constructed to feed fuel contained in a fuel tank to a fuel injection valve 3 (a fuel injector) that is capable of injecting the fuel to an engine 4 (an internal-combustion engine). The fuel feeder passage LF1 communicates between the fuel pump 1 and the fuel injection valve 3. The fuel feeder passage LF2 is branched from the fuel feeder passage LF1 so as to communicate with the pressure control valve 2. The back pressure generating passage LC is branched from the fuel feeder passage LF1 so as to communicate with the fuel tank. The pressure control valve 2 is arranged and constructed to control a pressure of the fuel fed to the fuel injection valve 3 (i.e., a pressure of the fuel in the fuel feeder passages LF1 and LF2). This pressure will be referred to as “a fuel pressure.”
The pressure control valve 2 includes a back pressure chamber 2r, a pressure controlling chamber 2c, a diaphragm 2B3 disposed between the chambers 2r and 2c, and a valve portion 2B attached to the diaphragm 2B3. The back pressure chamber 2r communicates with the back pressure generating passage LC, so as to be applied with a (fuel) back pressure P1 intermediate between the fuel pressure and a tank interior pressure when the solenoid valve S is opened. The pressure controlling chamber 2c communicates with the fuel feeder passage LF2, so as to be applied with the fuel pressure. Further, the valve portion 2B is capable of controlling a pressure of the fuel in the controlling chamber 2c to two control pressures (high and low control pressures) depending on whether the back pressure P1 is applied to the back pressure chamber 2r. 
When the solenoid valve S is opened, the back pressure chamber 2r is applied with the back pressure P1 (a high pressure). As a result, the pressure of the fuel in the pressure controlling chamber 2c can be controlled to the high control pressure because of the high pressure within the back pressure chamber 2r. Thus, the fuel pressure (the pressure in the fuel feeder passages LF1 and LF2 communicating with the pressure controlling chamber 2c) can be controlled to the high control pressure. Conversely, when the solenoid valve S is closed, the back pressure chamber 2r is applied with a limited or low pressure because the back pressure chamber 2r is not applied with the back pressure P1. As a result, the pressure in the pressure controlling chamber 2c can be controlled to the low control pressure because of the low pressure within the back pressure chamber 2r. Thus, the fuel pressure can be controlled to the low control pressure.
However, according to the pressure control valve 2, when the back pressure P1 applied to the back pressure chamber 2r is changed or fluctuated, the pressure in the pressure controlling chamber 2c can be proportionally changed depending on the applied back pressure P1 because the back pressure P1 is directly applied to the diaphragm 2B3. Therefore, if the back pressure P1 applied to the back pressure chamber 2r is excessively increased, the pressure in the pressure controlling chamber 2c may be excessively increased beyond the high control pressure. This means that the pressure in the pressure controlling chamber 2c cannot be accurately controlled to the high control pressure. As a result, the fuel pressure cannot be accurately controlled. This may lead to an inferior controllability of the fuel pressure.